Polymers are commonly used in oral care products such as toothpaste, not only as viscosity modifiers, but also to inhibit biofilm and plaque formation, to enhance the delivery and effectiveness of active ingredients, and to alleviate conditions such as dry mouth (xerostoma).
The precise interactions between polymers and tooth surfaces can be unpredictable, particularly when the teeth are coated with saliva and/or biofilm, as there may be complex interactions between the polymer, the proteins in the saliva, the biofilm, other ingredients in the oral care formulation, and the tooth surface. Different types of polymers may have different functional groups, which can participate in hydrogen bonding or ionic bonding to facilitate deposition and retention of the polymer on the tooth surface, but which may also interact with proteins in the saliva, biofilm, and other ingredients in the oral care formulation.
While it may be possible to predict in general terms that a particular type of polymer would be useful for a particular application, it may be more difficult to select exactly which of the many variants of that polymer type would be optimal. For many polymers, there is a large choice of different brands or grades of polymers of produced from the polymerization of the same monomer, each having differences in molecular weight, degree of substitution and/or crosslinking, and other properties that could affect optimal deposition and retention on the tooth surface.
Measuring polymer deposition on saliva-coated hydroxylapatite (scHAP) disks using current methods requires that the discs be exposed to polymer, washed, then the polymer is removed, e.g., by solvent extraction, and subsequently quantified by high-performance liquid chromatography (HPLC). This process is indirect, time consuming and provides no information about potential active-substrate interactions. It is of course possible to make formulations comprising various test polymers and evaluate performance in vivo, but this is time consuming and expensive as an initial screening method. There is a need for an assay that can rapidly and efficiently assess and quantify polymer deposition and retention on dental surfaces in vitro in order to screen and identify optimal polymers for use in oral care products.
Near-infrared spectroscopy (NIRS) is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum (from about 700 nm to 2500 nm). It has been used in a variety of applications, but not to measure polymer deposition on dental surfaces or to screen polymers for use in oral care products.